Several methods have been described in the literature for analyzing, assaying, recovering or extracting elements, especially precious elements, from ores. For example, when attempting to ascertain the total gold content of an ore sample, a so-called fire assay process is typically used. See, e.g., Kallmann, S. and Maul, C., "Referee Analysis of Precious Metal Sweeps and Related Materials," Talanta, 30(1):21-39 (1983). In the fire assay process, metals are dissolved and extracted using molten lead. The lead and precious metals are separated in a secondary process called cupellation and then the gold content of the precious metals collected in the fire assay process is determined using a variety of analytical techniques. When using the fire assay process on a so-called complex or refractory ore to determine total elemental content, the results achieved typically lead to the conclusion that no economically feasible recoverable elements, especially precious elements, e.g. gold, are contained therein. It would be beneficial if the amount of elemental values assayed and/or recovered from complex or refractory ores could be increased through an economically/commercially feasible method.
The problems associated with the extraction of elements, especially so-called precious elements, e.g., transition elements, base metals, lanthanides and the like, from complex or refractory ores are well known. Generally, conventional methods have been limited to recovering precious metal values, such as gold, on the order of about 0.05 troy ounces per ton of ore or less. Further, thermal-based methods, such as high-temperature roasting and thermiting, whereby precious metal ions in refractory ores are reduced, have led to undesirable formation of alloys with predominating natural based metals, such as Fe and Cu. These high temperature-formed alloys are highly refractory such that any precious metal values contained therein are typically extracted with great difficulty when subjected to subsequent smelting or hydrometallurgical treatment. In addition, chemical methods using a variety of lixivants, such as cyanide heap leaching, which uses environmentally unfriendly NaCn, have been used, but with scant results.
Accordingly there remains a need for better and reliable methods that are capable of making metals contained in materials, such as complex or refractory ores, assayable, analyzable or otherwise detectable using conventional techniques. In addition, there is a need for economical and commercially feasible methods for recovering or extracting elements, especially precious metal elements, from materials such as low grade, complex or refractory ores, including, without limitation, basaltic ores, alluvial ores and the like.